1. Technical Field
This invention is directed to the field of textile dyeing and in particular to the dyeing of textiles by the exhaust method using fiber reactive dyes containing the fiber reactive vinyl sulfone group.
2. Background
The exhaust method of dyeing is a batch method comprising the immersion of the textile goods in an aqueous solution of dye and various dyeing auxiliary chemicals. The goods are held in the dye bath for a predetermined time usually at an elevated temperature until the dye migrates into and fixes to the fiber. The exhaust dyeing method is well known in the art of coloring textiles; exemplary exhaust dyeing procedures are beck, jig, winch, jet and circulating liquor machine procedures.
In the exhaust dyeing method using fiber reactive vinyl sulfone dyes, one necessary auxiliary chemical is an electrolyte which is added to the dye bath to force the dye to migrate from the solution to the fiber. The most commonly used electrolyte is an inorganic salt such as sodium sulfate or sodium chloride. In exhaust dyeing procedures, this electrolyte is generally employed in amounts from about 20-50 grams per liter to about 100 grams per liter of dye bath with the amount of electrolyte being proportionally higher as the amount of dye employed in the dyeing increases. However, a few fiber reactive dyes are known which are used at reduced electrolyte concentration. After the dyeing process is completed, the exhausted dye bath solution is discharged to waste water treatment facilities for removal of electrolyte and other residual dye bath chemicals.
The present invention provides a method for the exhaust dyeing of textiles using a select class of dyes at significantly lower levels of electrolyte in the dye bath with the attendant reduction in raw materials costs, reduced chemical discharge to the environment and reduced waste water treatment costs. An additional advantage is that the process of the invention unexpectedly gives a higher dyeing efficiency as evidenced by the achievement of higher dye build up values.